A microcomputer is described in our European Patent Specification No. 0110642 which includes scheduling means to permit the processor to share its processing time between a plurality of concurrent processes. A linked list of scheduled processes awaiting execution may be formed. A currently executing process may be descheduled and processes may be scheduled by adding to a scheduled list when required. This may for example arise in effecting message transmission between two processes where it is required that both processes be at corresponding stages in their program sequence when the message transmission occurs. However that patent specification does not describe the use of time dependent processes wherein scheduling of a process may be effected in accordance with a specfified time for the process.